minecraft_lzstools/data/lzstools/predicate/unbreaking/offhand/all.json

{
    "type": "minecraft:entity_properties",
    "entity": "this",
    "predicate": {
        "equipment": {
            "offhand": {
                "predicates": {
                    "minecraft:enchantments": [
                        {
                            "enchantment": "minecraft:unbreaking",
                            "levels": {
                                "min": 1,
                                "max": 3
                            }
                        }
                    ]
                }
            }
        }
    }
}